Electric machines are utilized in a wide variety of applications. For example, hybrid/electric vehicles (HEVs) typically include an electric traction drive system that includes an alternating current (AC) electric machine which is driven by a power converter with a direct current (DC) power source, such as a storage battery. Machine windings of the AC electric machine can be coupled to inverter sub-modules of an inverter module. Each inverter sub-module includes a pair of switches that switch in a complementary manner to perform a rapid switching function to convert the DC power to AC power. This AC power drives the AC electric machine, which in turn drives a shaft of the HEV's drivetrain.
In many systems, the inverter modules are driven by switching vector signals that are generated based on voltage command signals. The voltage command signals are generated based on current command signals that are provided from a torque-to-current mapping module. In such systems, the torque-to-current mapping module receives a torque command signal (Te*), an angular rotation speed (ωr) of the machine, and a DC input voltage (VDC) as inputs, and maps these inputs to current commands that will ideally cause the machine to generate the commanded torque (Te*) at a given machine speed (ωr).
In controlling torque of an asynchronous machine (e.g., induction machine), it can be difficult to achieve high machine efficiency and a fast torque response. This is due, in part, to the inherent lagging characteristics of the rotor flux with respect to the stator current.
To improve machine efficiency, one conventional approach is to set current command slew rates to relatively lower values than would be used in comparison to current command slew rates that are used to control synchronous machines (e.g., permanent-magnet machines). However, setting slew rates to lower values can prevent a fast torque response, which is desirable in many induction machines. One way to do achieve a faster torque response is to maintain the rotor flux at a constant value above a certain level. However, this approach can reduce machine and/or inverter efficiency since it is necessary to maintain a certain level of current through the machine/inverter.
It would be desirable to provide improved methods, systems and apparatus for generating torque commands and/or current commands used to control an asynchronous machine such as an induction machine. It would also be desirable if such methods, systems and apparatus can provide a fast torque response while achieving acceptable levels of efficiency. Other desirable features and characteristics of the disclosed embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.